Cyclic process for the efficient generation of chlorine dioxide in dilute solutions

Abstract

An efficient cyclic process and related compositions for the in-situ generation of chlorine dioxide from dilute solutions of chlorite anions at near neutral pH. The cyclic process provides a means of safe and effective use of chlorine dioxide with reduced concern of chlorite accumulation in the aqueous system. The disclosed chemistry used to support the cyclic process can be applied independently or in various combinations that are effectively inert. This dramatically reduces safety concerns since the chlorine dioxide is produced in-situ to the application and in dilute concentrations. Also, the process allows for regeneration of inert anions such as bromide and chlorite thereby reducing operating cost.

1. A cyclic process for the in-situ generation of chlorine dioxide from a dilute solution of chlorite anions in a recirculating aqueous system treated with a chlorite anion donor, and wherein the said aqueous system remains substantially free of chlorite anions, the process comprising:
 addition of an activating oxidant selected from at least one of a free halogen donor comprising at least some portion of free chlorine and peroxymonosulfate donor to the said aqueous system; and 
 
       sustaining in said aqueous system a bromide anion concentration from about 10 ppm to 1000 ppm by addition of an alkali metal salt of bromide, a chlorite anion concentration necessary to sustain from about 0.2 to 1.0 ppm as chlorine dioxide by addition of an alkali metal salt of chlorite, and a pH of between about 6.8 to 8.0; whereby the activating oxidant reacts with the bromide anion to sustain a free bromine concentration from about 1.5 to 25 ppm reported as Br 2 , subsequent reaction of the free bromine with the chlorite anion to produce chlorine dioxide; and
 wherein at least some portion of the recovered bromide anions and chlorite anions resulting from the reduction of free bromine and chlorine dioxide are recycled in the cyclic process. 
 
     
     
       2. The process of  claim 1 , wherein the recirculating aqueous system is an aquatic facility. 
     
     
       3. The process of  claim 1 , wherein the recirculating aqueous system is a cooling tower. 
     
     
       4. The process of  claim 1 , wherein the recirculating aqueous system is a poultry washing system. 
     
     
       5. The process of  claim 1 , wherein the recirculating aqueous system is a vegetable washing system. 
     
     
       6. A cyclic process for the in-situ generation of chlorine dioxide from a dilute solution of chlorite anions in a recirculating aqueous system treated with a chlorite anion donor, and wherein the said aqueous system remains substantially free of chlorite anions, the process comprising:
 addition of an activating oxidant comprising peroxymonosulfate donor to the said aqueous system; and 
 
       sustaining in said aqueous system a bromide anion concentration from about 5 ppm to 500 ppm, a chlorite anion concentration necessary to sustain from about 0.2 to 1.0 ppm as chlorine dioxide by addition of an alkali metal salt of chlorite, and a pH of between about 6.8 to 8.0; whereby the activating oxidant reacts with the bromide anion to sustain a free bromine concentration from about 0.5 to 25 ppm reported as Br 2 , subsequent reaction of the free bromine with the chlorite anion to produce chlorine dioxide; and
 wherein at least some portion of the recovered bromide anions and chlorite anions resulting from the reduction of free bromine and chlorine dioxide are recycled in the cyclic process. 
 
     
     
       7. The process of  claim 6 , wherein the recirculating aqueous system is an aquatic facility. 
     
     
       8. The process of  claim 6 , further comprising sustaining from about 10 to 500 ppb measured as elemental metal of a transition metal catalyst that converts some portion of the peroxymonosulfate donor to sulfate free radicals. 
     
     
       9. The process of  claim 8 , wherein the transition metal catalyst comprises cobalt. 
     
     
       10. The process of  claim 8 , wherein the transition metal catalyst comprises ruthenium. 
     
     
       11. The process of  claim 8 , wherein the transition metal catalyst comprises iron. 
     
     
       12. The process of  claim 6 , further comprising addition of a chelating agent. 
     
     
       13. A cyclic process for the efficient conversion of a dilute solution of chlorite anions to chlorine dioxide in an aqueous system for enhanced inactivation of microbiological organisms, the process comprising:
 addition of an activating oxidant selected from at least one of a free halogen donor comprising some portion of free chlorine and peroxyxnonosulfate donor to the aqueous system; and 
 
       sustaining in said aqueous system a bromide anion concentration from about 5 ppm to 1000 ppm, a chlorite anion concentration necessary to sustain from about 0.2 to 20 ppm as chlorine dioxide by addition of an alkali metal salt of chlorite, and a pH of between about 6.0 to 8.5; whereby the activating oxidant reacts with the bromide anion to sustain a free bromine concentration from about 0.5 to 50 ppm reported as Br 2 , subsequent reaction of the free bromine with the chlorite anion to produce chlorine dioxide while sustaining a residual chlorite anion concentration of no greater than 50 wt % of the concentration of measured chlorine dioxide; and
 wherein at least some portion of the recovered bromide anions and chlorite anions resulting from the reduction of free bromine and chlorine dioxide are recycled in the cyclic process. 
 
     
     
       14. The process of  claim 13 , wherein the aqueous system is a cooling tower system. 
     
     
       15. The process of  claim 13 , wherein the aqueous system is a laundry washing machine. 
     
     
       16. The process of  claim 13 , wherein the aqueous system is a vegetable washing system. 
     
     
       17. The process of  claim 13 , wherein the aqueous system is a poultry washing system.